Did he sound young to be a captain? (4)
I believe the answer is:
kidd
'he sound young to be a captain?' is the definition.
The definition suggests a singular noun which matches the answer.
'did' is the wordplay.
I cannot really understand how this works, but
an anagram of 'did' is 'idd' which is within the answer.
A single letter 'k' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for kidd that I've seen before include "Captain --, Scots pirate" , "Captain William -, Scottish pirate" .)